At least six people died after gunmen opened fire inside a carwash in the Gulf coast port of Coatzacoalcos, authorities in Mexico's Veracruz state said on Thursday.The attackers left behind a message claiming responsibility for the assault on behalf of the Zetas cartel and threatening further violence against the rival Jalisco Nueva Generacion group, Efe news agency reported.Five people were pronounced dead at the scene and a sixth victim died at a nearby hospital.State police seized a vehicle left inside the carwash.More than 1,500 people have died in drug-related violence in Veracruz state during the past 11 months.Nationwide, homicides climbed by 62 per cent in the first 10 months of this year, according to figures published by the National Public Safety System.The Zetas, Jalisco Nueva Generacion and the Gulf cartel are battling in Veracruz to control not only the drug trade, but other criminal activities such as human trafficking, kidnapping and protection rackets.Veracruz, the heartland of the Mexican oil industry, is also an important agricultural region and boast the country's second-busiest cargo port.